Speed would not be any worse than the common Canon 400/5.6 and DA300 performs nicelly even on a Q so guess there's enough resolution to take from.

I don`t question the resolving power of the DA* 300
But it was kinda late for me last night, after a good night rest the technical side of brain is awake again.
SDM is in the lens, right? So the TC only provides/passes the power for the in-lens system and therefore speed should be the same as without the TC.

I`m not familiar with the Canon 400L f5.6 but Canon`s AF is still (miles) ahead of Pentax. Is this a particulary slow focussing lens?

If you put this on a FF with a DA21/3,2 you'll have exactly a 29,4/4,48. I don't see any interest to have a 30mm F/4,5 on a fullframe body. I'd buy a cheaper M28/3,5 and surely would have a better image quality.

Regards to an earlier question. TC usually only makes sense with tele lenses, to get a focal length that you otherwise couldn't (because it isn't in production or it costs significantly more than a TC and slightly wider lens or the longer lens is big and unwieldy). To use a TC on a 21mm, in terms of FoV, doesn't make sense. Better to buy another lens. But! I think the question was about the image circle. The question is whether this TC enlarges the image circle (and makes it too big for the sensor to use fully), or if it keeps it the size of APSC (which makes sense, because then you have less useless light bouncing in the camera). And I don't know the answer to this question, not for this specific product.

I`m not familiar with the Canon 400L f5.6 but Canon`s AF is still (miles) ahead of Pentax. Is this a particulary slow focussing lens?

I reject that statement until I see a credible AF test between a K-3 and 7D.

The DA*300 is fast enough for anything I've done, including BIF and hockey. I owned a Sigma 150-500 and the DA*300 is faster than the HSM on that lens. I don't see why a TC would slow it down, all it has to do is faithfully conduct the electronic signal between the camera and lens.

The T/C will slow down the af of any lens just because it's halving the light density. Canon and Pentax would be equally affected in theory; in practice Pentax's huge AF sensors would likely be less affected.

I reject that statement until I see a credible AF test between a K-3 and 7D.

The DA*300 is fast enough for anything I've done, including BIF and hockey. I owned a Sigma 150-500 and the DA*300 is faster than the HSM on that lens. I don't see why a TC would slow it down, all it has to do is faithfully conduct the electronic signal between the camera and lens.

IMHO a comparison between the K3 and the 7D would be apples vs oranges, not only because they don`t share the same lenses but also because of the ageing 7D. Even when it is a draw, that`s quite impressive for an allmost 5 year old body

Well, it slows down because you`re loosing light. A 1.4 T/C will cost you 1 stop of light, a 1.7 TC costs 1½ stop and a 2x TC will cost you 2 stops so a DA*300 with 1.4x TC will behave like a 420mm F5.6. From what I understand is that most AFsensors work upto F5.6 (except a few high-end bodies that will go upto F8) and when going over that limit you will loose AFcapability.

Regarding the 150-500: I still have it and in terms of speed it`s no match for my screwdiven 100-300F4, even with the sigma 1.4x EX DG T/C.

Originally posted by ElJamoquio

I've never seen a credible af test of anything.

The T/C will slow down the af of any lens just because it's halving the light density. Canon and Pentax would be equally affected in theory; in practice Pentax's huge AF sensors would likely be less affected.

I have, FNAC Laboratoires. I haven't seen any tests beyond the K-5, but of the results I have seen, the K-x, K-r and K-5 have similar performance to comparably priced and contemporary Canons and Nikons. The K-5 was equal to the D7000, the 7D and D300 beat all other APS-C bodies in AF-C mode (K-5, D7000, 60D).

IMHO a comparison between the K3 and the 7D would be apples vs oranges, not only because they don`t share the same lenses but also because of the ageing 7D. Even when it is a draw, that`s quite impressive for an allmost 5 year old body

The 7D still beats the 70D for continuous auto-focus and burst mode. If the Canons you were referencing as being miles ahead in AF are Full Frames, then I won't argue. For APS-C, I don't believe it.

Originally posted by TenZ.NL

Well, it slows down because you`re loosing light. A 1.4 T/C will cost you 1 stop of light, a 1.7 TC costs 1½ stop and a 2x TC will cost you 2 stops so a DA*300 with 1.4x TC will behave like a 420mm F5.6. From what I understand is that most AFsensors work upto F5.6 (except a few high-end bodies that will go upto F8) and when going over that limit you will loose AFcapability.

You are talking about Canon. Pentax AF is not limited to f5.6 or f8 and will work beyond that. With a DA*300, you lose a stop, from f4 to f5.6. That may affect whether the camera can find focus in some extreme or marginal condition, but not the speed at which the AF moves. The main complaint with SDM is that it moves the lens elements too slowly, especially with the portrait lenses; DA*55 and DA*50-135mm. I'm pretty certain the DA*300 is as fast as a screw drive or competitors' standard micro-motor lenses. It is slower than expensive ring drive lenses.

Note that when stopping down a DA*300 to f8 with a TC mounted, the effective f-stop is f/11, but the focussing is done with the aperture wide open, at f5.6.